Generally, in mobile communication by the DS-CDMA system, even if each mobile station (mobile communication terminal) performs a transmission with the same transmission power in an up link from the mobile station to a base station, because distances and propagation environments from respective mobile stations to the base station are different, the so-called far-and-near problem in which the transmission signal of a mobile station located at a position near the base station masks the transmission signal of a mobile station located at a position distant from the base station occurs.
Consequently, it is important in the mobile communication by the DS-CDMA system to control the transmission power of each mobile station in order that reception signal levels from all of the mobile stations may be fixed at the base station.
As the methods of transmission power control in mobile stations in the mobile communication by the DS-CDMA system, there are an open loop transmission power control method and a closed loop transmission power control method.
The open loop transmission power control method is a method in which a mobile station itself variably controls its transmission power according to the field levels (reception field levels) of reception signals from a base station. In the open loop transmission power control, a wide range variable control of more than 10 dB is performed at one time of control in order to obtain desired transmission power. It is necessary in the open loop transmission power control to ensure the absolute value of the transmission power.
On the other hand, the closed loop transmission power control method is a method in which a base station performs a closed loop control for ensuring the output levels of up link signals between mobile communication terminals and the base station in order that the reception levels of the up link signals from the mobile stations may be fixed. That is, the base station generates a Transmit Power Control (TPC) command on the basis of the reception result of an up link signal from a mobile station, and transmits the generated TPC command to the mobile station to perform the variable control of the transmission power of the mobile station.
In the closed loop transmission power control, in each mobile station, a narrow range variable control by a level in the range of from one to three dB is performed on the basis of the TPC commands from the base station to perform an adjustment to a desired transmission power. In the closed loop transmission power control, it is necessary to ensure relative values of the transmission power of the mobile stations.
Incidentally, a transmission output circuit of a conventional mobile communication terminal in the DS-CDMA system to which the above-mentioned open loop transmission power control method or the closed loop transmission power control method is applied is configured, for example, as shown in FIG. 13. The transmission output circuit of FIG. 13 will be described in the following.
In FIG. 13, 100 designates a transmission signal processing system of a mobile communication terminal by the DS-CDMA system, and 200 designates a transmission power control system.
The transmission signal processing system 100 performs the up conversion of an input transmission signal in an intermediate frequency band (hereinafter referred as an IF band transmission signal) Sif, which was performed a spread spectrum processing and a predetermined orthogonal modulation, to a radio frequency (RF) band transmission signal, and further, applies a power amplification to the RF band transmission signal, supplies to an antenna 1 through an antenna connector end 2, and transmits the RF band transmission signal to a base station.
Then, the transmission signal processing system 100 performs the automatic gain control (AGC) of the IF band transmission signal and the RF band transmission signal by means of an AGC signal from the transmission power control system 200, and thereby controls the electric power of the transmission signal to be a desired power. The more detailed configurations and the processing operations of the transmission signal processing system 100 will be described in the following.
That is, the IF band transmission signal is supplied to an IF band AGC amplifier 101, and amplified while performing the gain control of the IF band transmission signal by means of an IF band transmission signal AGC voltage IFagc supplied from the transmission power control system 200 through an D/A converter 102.
The IF band transmission signal amplified by the IF band AGC amplifier 101 is limited its band by an IF band band pass filter (IF band BPF) 103, and then is supplied to a mixer circuit 104. In the mixer circuit 104, the IF band transmission signal is mixed with a local frequency signal from a local oscillation unit 105 and is performed the up conversion to a frequency signal in the RF band (hereinafter, referred to as an RF band transmission signal).
The RF band transmission signal from this mixer circuit 104 is amplified while performing the gain control by means of an RF band AGC voltage RFagc supplied from the transmission power control system 200 through a D/A converter 107 in an RF band AGC amplifier 106. After the amplified RF band transmission signal is limited its band by an RF band band pass filter (RF band BPF) 108, the RF band transmission signal is supplied to a power amplifier 109, and is amplified to a predetermined electric power.
The RF band transmission signal, the electric power of which was amplified by the power amplifier 109, is transmitted to the antenna connector end 2 through an isolator 110 and a duplexer 111, and is transmitted from the antenna 1.
Transmission power control data Cif and Crf, which are digital data as bases of the above-mentioned IF band transmission signal AGC voltage IFagc and the RF band transmission signal AGC voltage RFagc, are generated by the transmission power control system 200 in the way to be described in the following.
The transmission power control system 200 includes a transmission power control data processing unit 201, a transmission power control data table memory 202 which stores a transmission power control data table, and a transmission power control data correction table memory 203 which stores a transmission power control data correction table. The transmission power control data processing unit 201 is composed of, for example, a Digital Signal Processor (DSP).
In the transmission power control data table memory 202, transmission power control data, which becomes optimum to various values of the transmission power output level of the transmission signal intended to be transmitted and instructed by instruction data Po under environmental conditions such as a predetermined power supply voltage, a temperature, a transmission frequency, and the like, is written as the transmission power control data table in the way which will be described later.
Moreover, in the transmission power control data correction table memory 203, information of the transmission power control data correction table for correcting each transmission power control data written in the transmission power control data table according to parameters such as the environmental conditions is written in the way which will be described later.
In the conventional case, as the parameters for the transmission power control data correction table, an environmental temperature (an ambiance temperature) at the use of the transmission output circuit, the power supply voltage and the frequency of the transmission signal are used.
Then, the transmission power control data processing unit 201 in the transmission power control system 200 receives the voltage of a power supply 112 of the power amplifier 109, the information of the ambiance temperature of the mobile communication terminal in which the transmission signal processing system 100 is mounted, and the information Fx of a transmission frequency from a not shown communication control unit, which are the parameters. The transmission power control data processing unit 201 further receives the instruction data Po instructing the transmission power output level of a transmission signal intended to be transmitted, and refers to the tables in the transmission power control data table memory 202 and the transmission power control data correction table memory 203 to operate the transmission power control data Cif and Crf which are optimum to the transmission power output level of the transmission signal intended to be transmitted. Then, the transmission power control data processing unit 201 outputs the operated transmission power control data Cif and Crf.
Hereupon, after the voltage of the power supply 112 of the power amplifier 109 is converted to digital data by an A/D converter 113, then the converted digital data is supplied to the transmission power control data processing unit 201 in the transmission power control system 200. Moreover, a temperature sensor 114 is provided in the transmission signal processing system 100 and the temperature information in the vicinity of the transmission signal processing system 100 which was detected by the temperature sensor 114 is converted to digital data by the A/D converter 113, and then thus converted digital data is supplied to the transmission power control data processing unit 201 of the transmission power control system 200.
FIG. 14 is a diagram for explaining the writing of the information in the transmission power control data table into the transmission power control data table memory 202, and the writing of the information in the transmission power control data correction table into the transmission power control data correction table memory 203.
As to the information in the transmission power control data correction table, the correction data of the transmission power control data to temperature changes, power supply voltage changes, transmission frequency changes as the parameters is previously produced at the stage of designing and/or the stage of developing the transmission output circuit or the mobile communication terminal. Then, the produced correction data of the transmission power control data is written into the transmission power control data correction table memory 203 through an external interface (external I/F) 204 as the transmission power control data correction table by means of a control data writing unit 21 shown in FIG. 14 on an adjustment line at the time of mass production of the transmission output circuit, or on an adjustment line at the time of mass production of the mobile communication terminal which mounts the transmission output circuit thereon.
The information in the transmission power control data table is a correspondence table of various target transmission power output levels pertaining to a transmission signal in a predetermined environmental condition and the transmission power control data to the transmission power output levels. The writing of the transmission power control data table into the transmission power control data table memory 202 is executed as follows.
A certain target transmission power output level is supposed. While the RF band transmission signal output from the antenna connector end 2 is monitored with a power meter and a transmitter tester 22, the transmission power control data is adjusted in order that the RF band transmission signal output may take the target transmission power output level. When the RF band transmission signal output takes the target transmission power output level, the transmission power control data at that time is written into the transmission power control data table memory 202 as the transmission power control data corresponding to the target transmission power output level. By performing the operation described above to all of the values of the necessary target transmission power output levels, the transmission power control data table is written into the transmission power control data table memory 202.
At the time of the writing, the ambient temperature, the voltage of the power supply 112, the frequency of the RF band transmission signal, and the like at the time of the writing of the transmission power control data are held in the transmission power control data table memory 202 as standard parameter information. Otherwise, the standard information is held by the transmission power control data processing unit 201.
As described above, the transmission power control data processing unit 201 outputs the transmission power control data Cif and Crf being the digital data to be the bases of the IF band transmission signal AGC voltage IFagc and the RF band transmission signal AGC voltage RFagc using the table information written in each of the table memories 202 and 203 as follows.
First, the transmission power control data processing unit 201 refers to the signal Po instructing the transmission power output level of the transmission signal which is intended to be transmitted and is supplied to the transmission power control data processing unit 201, and extracts the transmission power control data which makes it to be the transmission power output level from the transmission power control data table in the transmission power control data table memory 202.
Next, the transmission power control data processing unit 201 compares the digital data of the power supply voltage from the A/D converter 113, the digital data of the temperature information detected by the temperature sensor 114 from the A/D converter 115, and the information Fx of the transmission frequency with the above-mentioned standard data related to the transmission power control data table, and on the basis of the comparison result, the transmission power control data processing unit 201 extracts suitable transmission power control data correction data from the transmission power control data correction table in the transmission power control data correction table memory 203.
Then, the transmission power control data processing unit 201 operates the optimum transmission power control data to the output level at which transmission is intended to be performed on the basis of the data value of the transmission power control data obtained from the transmission power control data table memory 202, the present power supply voltage, and the data information of the temperature and the transmission frequency. As the transmission power control data, as described before, the IF band AGC data IFagc and RF band AGC data RFagc are severally operated, and then they are transferred to the D/A converters 102 and 107.
Thus, the transmission power control data processing unit 201 generates the transmission power control data Cif and Crf from which the influences of the environmental parameters such as the temperature, the power supply voltage, the using frequency and the like in the actual usage environmental condition are removed. Then, the AGC control of transmission signals is performed at the AGC amplifiers 101 and 106 by means of the AGC voltages IFagc and RFagc, which are the D/A conversion outputs of the transmission power control data Cif and Crf, and thereby the transmission signal is controlled in order that the target desired transmission power can be obtained from the power amplifier 109.
As described above, the transmission power control method of the transmission output circuit of the conventional mobile communication terminal adopts a correction table in which correction values to frequency changes, temperature changes and power supply voltage changes are severally written on adjustment lines at mass production in advance, and thereby performs a transmission power control by a feed forward system which compensates the transmission power according to ambient environment changes.
However, in the case where the above-mentioned conventional transmission power control method is actually applied to the mobile communication system by the DS-CDMA system, the following problems exist.
Because the conventional transmission power control shown in FIG. 13 is the feed forward system as described above, it is not examined whether the electric power of an actually transmitted transmission signal takes the target transmission power output level correctly or not. Consequently, there is no assurance of the output of the power amplifier 109 taking the target desired transmission power output level. Consequently, if any abnormality of transmission power or erroneous transmission is caused when each part constituting the transmission signal processing system 100 such as the power amplifier 109, the Rf band AGC amplifier 106 and the like is out of order, the conventional method can not detect it.
The abnormality of the transmission power in the mobile communication system by the DS-CDMA system causes defects such as the interference with other users, nonarrival of an up link signal to a base station in a fringe area of a cell, and the like.
On the other hand, in the Third Generation Partnership Project (3GPP) Standards and the TELEC Standards in Japan, there are regulations concerning the items pertaining to the maximum transmission power and the minimum transmission power (the items of the deviation of antenna power) as the transmission characteristics of the mobile communication terminal by the DS-CDMA system.
The items pertaining to the maximum transmission power regulate the ability for transmitting the maximum transmission power defined on the basis of the power class of mobile devices of the mobile communication terminal while keeping the maximum transmission power within a regulated level range. Moreover, the items pertaining to the minimum transmission power similarly regulate the minimum transmission power defined on the basis of the power class of mobile devices of the mobile communication terminal.
When a mobile communication terminal by the DS-CDMA system especially performs a transmission at the maximum transmission power, it is necessary to compensate the quantities of variations of the RF active components of the transmission signal processing system 100 such as the power amplifier, the RF band AGC amplifier, the IF band AGC amplifier and the like to the environmental condition changes such as the frequency, the power supply voltage, the temperature and the like.
In addition, in the case where the mobile communication terminal is mass-produced, due to dispersion among individual parts, even if the correction table to the frequencies, the power supply voltages and the temperatures which are uniquely determined at the stage of designing or development is provided like conventional embodiment, some deviations from the information in the correction table are produced in the above-mentioned transmission signal processing system 100.
That is, in the above-mentioned conventional transmission power control of a feed forward system, it is not easy to meet the standard values of the maximum transmission power in case of the mass-production of the mobile communication terminal. Moreover, it is also not easy to satisfy the standard values as to the minimum transmission power similarly.
Moreover, the DS-CDMA system mobile communication terminal uses a multi-code transmission for implementing a high speed data rate. Because a plurality of code channels are multiplexed by means of plural kinds of spread codes in the multi-code transmission, a peak power to the average transmission power changes according to the number of multiplexed channels. Accordingly, it is necessary to correct the transmission power output level according to a changed number of multiplexed channels when the number of multiplexed channels is changed.
However, as described above, the conventional transmission power control method by the feed forward system includes the correction table to the frequencies, the power supply voltage, and the temperatures, but does not include any correction table to the number of multiplexed channels. Moreover, even if the mobile communication terminal includes the correction table to the number of multiplexed channels, as described above, it is not easy to satisfy the standard values in the case where the number of multiplexed channels is changed when an up link signal is transmitted at the maximum transmission power or the minimum transmission power.
Then, in the case where the standard values of the transmission characteristic is not satisfied, as described above, the problems such as the decrease of the capacity of a cell based on the interference with other users, the nonarrival of an up link signal in a fringe area of a cell, and the like exist.
In this case, the mobile communication terminal performs adjustment to desired transmission power by means of the narrow range variable control based on the TPC control from the base station in the closed loop transmission power control. However, because the adjustment is performed by the step within the range of from one to three dB at the utmost, the problems continue for a while. Moreover, above all, not satisfying the standard values is a big problem as the mobile communication terminal.
This invention, in view of the problems described above, aims to provide a transmission output circuit capable of always performing accurate transmission power control, and capable of detecting the abnormality of transmission power which causes interference with other users and the failures of parts which cause erroneous transmission.